A preliminary assessment of geodynamic controls on depositional systems and sandstone diagenesis in back-arc basins, Western Pacific Ocean

Abstract

Nine depositional systems are recognized in cores recovered by the Deep Sea Drilling Project from the back-arc basins of the western Pacific. These systems include: submarine fan, debris flow, silty basinal turbidite, biogenic pelagic carbonate, resedimented carbonate, biogenic pelagic silica, pyroclastic, hemipelagic and turbid-layer clay, and pelagic clay depositional systems. The occurrence of these depositional systems in time and space is correlated with regional uplift and volcanism, climatic change, biological productivity, and critical relations of sediment yield from potential sources which experience sufficient uplift and development of an extensive drainage and erosional regimen. Debris flows and submarine fan systems tend to accumulate after uplift of andesitic volcanic arc sources following development of a regional drainage network. Biogenic pelagic systems tend to be controlled by biological productivity and are indicators of back-arc basin movement through such productivity zones by regional crustal shift. Hemipelagic and turbid-layer clay systems are derived from terrigenous sources and their volume is dependent on climatically-controlled sediment yield from such sources. Resedimented carbonate systems tend to occur during times of active basinal faulting. Volcaniclastic sandstones recovered in back-arc basin DSDP cores show evidence of diagenetic alteration in response to burial depth, temperature and thermally-driven fluid circulation. Younger sandstones tend to show pore-space reduction, rim cementation by chlorite and mixed-layer illite-smectite and pore-filling cementation by clinoptilolite. Downhole, pores are filled with heulandite and analcite. Older sandstones show pore-filling with sparry calcite and replacement of component minerals and rock fragments by calcite, chert and zeolites. The distinct age-depth zonation of diagenetic changes suggests that thermally-driven interstitial fluids combined with advection of ocean waters and basement waters accounts best for the mineralogical reactions observed.